1. Field of the Invention
The present invention relates to blood products and methods of preparation. More specifically, the present invention relates to the preparation of stabilized blood products using diafiltration.
2. Description of the Related Art
Platelets are anucleate cells that circulate in the blood in a resting form. They are the cellular component of the blood coagulation mechanism. Upon stimulation at a site of vascular injury, platelets adhere to the injured surface and undergo a complex series of biochemical and morphological alterations, resulting in secretion of stored granular components and formation of platelet aggregates. Platelet adhesion and aggregation, through interaction with fibrin, results in the formation of a primary platelet plug. Plasma coagulation is further accelerated by the increased availability of platelet membrane phospholipid surfaces that concentrate clotting factors and activate coagulant proteins at the injured hemorrhagic site.
Platelets currently are used in clinical settings to treat various conditions, including hemorrhagic shock and thrombocytopenia. Thrombocytopenia is characterized by an abnormally small number of platelets in the circulating blood. The condition can be induced in patients by heparin use, infections, auto-antibodies, malaria, lymphoma, hepatitis, radiation exposure, and chemotherapeutic agents.
Administration of a platelet preparation can also be utilized to treat certain genetic disorders that result in impaired platelet function. In addition, diafiltered stabilized blood product preparations can be used in the surgical repair of trauma involving extensive blood loss, such as for treatment of gun shot and knife combat victims.
Current therapeutic blood product transfusion therapy is hampered in the clinical setting by the short (five day) shelf life of liquid platelets or liquid blood cellular products (stored at 22.degree. C.), often producing a local shortage of supplies. Furthermore, current storage practices are conducive to bacterial growth and result in an increased incidence of platelet or blood cell transfusion-associated bacterial sepsis. Other problems associated with platelet transfusion therapy include febrile reactions and HLA (Human Leukocyte Antigen) alloimmunization due to white blood cell (WBC) contamination. Additionally, a risk of viral transmission exists with fresh platelet or blood cell transfusion therapy due to the absence of viral inactivation or removal steps.
The development of a platelet or blood cellular product that provides greater bacterial and viral safety and that has a longer shelf life thus would be advantageous. The ultimate goal is to produce a stabilized blood platelet or blood cellular product that is virally safe, WBC depleted, sterile, stable, and hemostatically effective. A stabilized diafiltered blood product that is storable at room temperature, is lightweight, durable, easy to transport, FDA approved, and has a shelf life of two to five years would be a significant advancement in the management of blood platelet and blood cellular resources. Such a product preferably would be made under Good Manufacturing Practice guidelines using a large-scale method capable of addressing the aforementioned issues and would be gentle enough to prevent extensive activation and aggregation of the platelets.
Lyophilized, or freeze-dried, platelet products are known which are produced using centrifugation methods. See U.S. Pat. No. 5,213,814 to Goodrich, Jr. et al., for example. See also Chao et al., Infusible platelet membrane microvesicles: a potential transfusion substitute for platelets, Transfusion 1996, which teaches a method of producing a lyophilized platelet membrane product. Reference also is made to pending U.S. patent applications Ser. No. 891,277, filed May 29, 1992, and Ser. No. 08/424,895, filed Apr. 19, 1995. Centrifugation undesirably causes activation of the platelets, and cannot be scaled up to production levels. Further, the known methods cannot be carried out under sterile conditions, and no viral reduction steps are present in the known methods.
Diafiltration is a known separation process that uses membranes to separate components in a liquid suspension based upon differences in particle size. Depending upon the pore size of the membrane, a component of the liquid suspension can be selectively retained or passed through the membrane. Diafiltration is employed routinely during non-blood cell harvesting applications to separate cells from the acellular medium, but never before has diafiltration been adapted to the production of a blood platelet or blood cellular product.
Accordingly, the need exists for a method to prepare a blood platelet or blood cellular product that does not involve platelet activation, can be scaled up to production levels, and that produces a product that is sterile and virally safe.